b 1. Field of the Invention
The present invention relates to phase-locked loop apparatus for producing adjustable microwave frequencies in the range of 7 to 10 gigahertz in steps of 5 to 10 megahertz. More specifically, the present invention relates to a computerized control multiple-loop phase-locked loop circuit employing a novel frequency synthesizer.
2. Description of the Prior Art
Frequency synthesizer systems are known and have been classified in U.S. Class 328, Subclass 14; and in Class 331, Subclasses 16, 22 and 19; and are further classified in International Class H03L 7/18 and 7/22.
Prior art basic linearized phase-locked loops are well known and include a VCO having an output coupled to a divide by N device, a mixer, a phase detector and a low pass filter in the loop and have an external reference frequency applied to the phase detector so that deviations of the VCO from the reference frequency cause the phase detector to generate an error voltage which when applied to the VCO adjust the VCO frequency to match the referencve frequency.
Multiple-loop phase-lock loops are known and have been employed in frequency synthesizing systems, however, such systems have heretofore been relatively complex, employed a plurality of N identical digit modules and complex circuitry similar to that set forth in U.S. Pat No. 4,626,787 and references discussed therein.
There is an unmet requirement for simple, low power, broad range frequency synthesizer which is capable of operating in the microwave frequency range. The frequency synthesizer apparatus needs to be compact, of light weight and easily controlled by a remote processor controller over small steps without the requirement of hardware modifications.